Probe-type thermostat



March 13, 1962 F. REINGRUGER 3,025,374 PROBE-TYPE THERMOSTAT Filed April 1e, 1957 zu i /9 INVENTOR.

3,025,374 Patented Mar. 13, 1962 3,025,374 PROBE-TYPE THERMOSTAT Frank Reingruber, Bartlett, N .H.

(Jackson, N.H.) Filed Apr. 16, 1957, Ser. No. 653,082 1 Claim. (Cl. 200-137) The invention herein disclosed relates to thermostats of the probe type wherein the switch or other mechanism to be controlled is actuated by a push rod of low thermal expansion characteristics encased within a tube of higher thermal expansion coeicient.

Among materials used for the low expansion element ceramics, because of low cost and availability, have been found particularly suitable. There are disadvantages, however, in the use of ysuch materials. Because of their brittle friable character, they are subject to fracture and breakage and being encased, the defect, rendering the thermostat inaccurate or-inoperative, might not be known.

Thus, a ceramic rod thermostat which may have been dropped or struck in some way might very well appear to be in perfect condition and yet be faulty to the extent of being inaccurate and unreliable or even entirely inoperative.

Objects of the present invention are to utilize the good yfeatures of the ceramic operation but to overcome and prevent the breakage and fracture heretofore usually appurtenant thereto.

Brieily, these objects have been accomplished by making the ceramic rod element in longitudinal sections coupled together with freedom of movement such as to take up and accommodate any blow that might fracture a rod in one continuous length.

Other important objects of the invention are to provide suitable self-centering and adjusting means for the ceramic thrust element, to provide proper operating connection between this rod and the switch mechanism, and to provide Calibrating adjustment which will hold to a fixed relation on the thermostat base regardless of angular adjustment for control purposes.

Other desirable objects attained by the invention and the novel features of construction, combination and relation of parts through which the purposes of the invention are accomplished are set forth or will appear in the course of the following specification.

The drawing accompanying and forming part of the specification is illustrative of a present commercial embodiment of the invention. The structure, however, may be modified and changedas regards the immediate illustration all within the true intent and scope of the invention as hereinafter defined and claimed.

FIG. 1 in the drawing is a plan view showing one of the thermostats attached in operative relation to an electric cooking utensil, the latter shown broken away.

FIG. 2 is a side elevation of the thermostat unit in operative relation, the utensil broken away and shown in section.

FIG. 3 is an enlarged plan View showing the parts of the unit as they lappear after removal of the top half of the insulating case forming the base or body of the device, the fastenings securing the two parts of the case together shown in section.

FIG. 4 is a broken longitudinal sectional View showing particularly the jointed `ceramic push rod.

FIG. 5 is a further enlarged broken longitudinal sectional view of the switch mechanism and sectional rod element.

FIGS. 6 and 7 are detail views of the adjustable switch spring.

In FIGS. 1 and 2, the temperature sensing probe of the unit is indicated at 1) entered in a thermometer well 11 provided in a cooking utensil 12, the latter containing an electric lheating element having terminal prongs 13, 14 engaged in terminal sockets 15, 16, FIG. 3 in the unit.

The case forming base of the unit is made up of co-mplemental top and bottom halves 17, 18 secured together by screws or other fastenings 19.

The probe 10 as shown in FIGS. 4 and 5, is made up of a tube 20 of brass or other thermally expansive metal and a rod of less expansive material connected with the extended end of the tube but free `for the balance of its length to actuate the switch or other mechanism.

In accordance with the present invention,the rod element is made of ceramic and instead of being only one continuous length, is in longitudinally extensive sections, two in number in this instance, designated 21 and 22.

These ceramic sections are jointed at their meeting ends by a coupling designed to hold them in alignment but to allow them limited freedom of movement so that under impact, they may rock or shift slightly enough to absorb the shock and overcome the tendency of breakage or fracture.

In a preferred form such as shown, the rod is of tubular formation and the coup-ling is in the form of a double ended stud 23 to enter the opposite ends of the tubular sections and having an intermediate annular flange 24 to stand between the adjoining ends of the sections.

This tubular structure is desirable for lightness and strength. In addition to the advantage of providing for an inserted double pin or stud form of coupling, it affords a convenient structure for centering and adjusting it in the expansion tube 20.

The centering and adjusting means is shown as a screw 25 entered in the free end of tube 20 and carrying a central stud 26 at the inner end engageable in the end of the ceramic tube.

After desired adjustment of the ceramic, the centering and adjusting screw 25 may be secured in the adjusted position by a spot of solder 27.

The inner end of the ceramic tube is shown as having flanged stud 28 entered therein, this stud having a rounded head 29 for centering engagement in the dimple socket 30 in the contact spring abutment 31. The studs in the opposite ends of the tubular ceramic thus hold it properly centered and preferably free of contact with the inner wa-ll of the containing tube 20.

At the inner end, the probe tube 20 is rigidly secured as by riveting and soldering at 32, FIG, 5, in the angular end abutment 33 of an inverted channel shaped frame 34. This frame forms the supporting base for the switch contacts and has at the opposite end an angularly turned abutment 35 which holds it seated in fixed relation in the cavity 36 provided for it in the lower half 18 of the base.

The switch is shown as made up of relatively stationary and moveable switch springs 37, 38 secured in insulated opposing relation in the top of the frame 34.

The lower switch spring is of special construction having an inclined intermediate portion 39 longitudinally slotted at 40 to render it freely flexible and having the angular abutment 31 of similar shape and welded or otherwise secured over the lower part of the inclined slotted portion, FIGS. 6 and 7.

This construction renders the movable switch spring quite sensitive and free to respond to the thrust and retraction of the ceramic element.

As will be clear in FIG. 5, the thrust against the bracket 31 extending angularly from the switch spring is applied over the slotted, inclined portion of the spring where it can be most effective to accomplish switching movements of the spring.

Calibration of the unit is effected in the illustration by ya rotary stem 41 having a screw mounting in the top of the frame or housing 34 and carrying an insulating button 42 at the lower end engageable with the top contact spring 37 for positioning it in respect to the lower thermostatically controlled spring 38.

This Calibrating screw extends up through an opening 43 in the top of the base and to keep this opening always closed against extraneous matter, the knob provided to turn the screw is slidingly keyed over the stem of the screw at 45 and is yieldingly pressed downward into close fitting sliding engagement wit-h the top of the base by a bowed spring 46 bearing down at opposite end on the bottom of a cavity 47 in the top of the knob and secured on the stem by a screw 4S.

The knob tensioning spring 46 is shown keyed at 49 on the splined portion of the stern so as to always turn with the stern and the screw 4S is shown as having a dependent annular fllange 50 at the rim of the same bearing on the spring to hold it always in keyed engagement on the stem. With this construction, the knob will be yieldingly held in sliding engagement with the top of the base while the stem moves up and down in its screw mounting in the supporting frame. Thus, the opening 43 in the top of the base will be kept closed at all times and lche `frictional engagement of the knob with the base will serve to hold the Calibrating screw in any position to which it may be adjusted.

The top of the knob is shown closed over by an indicating disc 51 carrying on and off, temperature indications or the like.

This indicating cover is shown in FIG. as seated in an annular cavity 52 in the top of the dial and as having tabs or prongs 53 struck downwardly in engagement with positioning openings provided in the knob.

For quick convenient reading of the dial, the top member of the base is shown as having a triangular pilot-light window 54 pointed toward the dial to serve as an index. The pilot lamp is shown at 55 in FIGS. 3 and 4.

The construction is relatively simple `for what it accomplishes and can be manufactured at reasonable cost. Making the lo-w expansion element in short sections connected by what may be considered universal joints of limited lateral extent permits the ceramic rods to in effect bend and thus yield rather than break. The connecting studs have loose fitting engagement in the opposing ends of the ceramic tube sections thus allowing slight lateral movement or deflection in any direction and the tube being held at opposite ends under compression will be maintained at constant length and with no possibility of the connecting stud coming loose or dropping out of either tube section.

The Calibrating knob is held by the spring 46 in close, fiat engagement against the top of the base in position Where it can be instantly read in connection with the pilot light window. The dependent flange or skirt 5G of the spring securing screw 48 is shown in `FlG. 5 as eX- tending down below the top of the screw stem 41, that is inwardly over the end of the stem so as to hold the Ft spring below the end of the stem and thus always engaged with the splines in the side ofthe stem.

The ends of this bowed spring engaged with the knob then act in the capacity of levers transmitting turning effort of the knob to the stem and taking part of the load of turning the stem off the splined or key connection 4S between the knob and the stern. The knob is usually of molded plastic which may become brittle through repeated heating and cooling, impairing the key connection between the knob and the splines or serrations on the stern. This possible loss of grip between the knob and stem is overcome by the yielding connection between the knob and the spring arms which have the sliding keyed connection with the stem.

What is claimed is:

A thermostat of the probe type comprising a supporting tube of relatively high thermal expansibility, ceramic tubes of lower thermal expansibility in longitudinally aligned `relation in said supporting tube, a coupling stud loosely engaged in opposing ends of said ceramic tubes, an ,adjusting screw engaged in one end of said supporting tube and having a projecting stud engaged in the end of the ceramic tube adjoining the same, means for sealing said screw inadjusted relation in the -supporting tube, a stud engaged in the end of the ceramic tube at the opposite end of the supporting tube, said last mentioned stud having a projecting rounded head, a switch spring having a rigidly secured base portion and a projecting spring arm oiiset from said rigidly secured base portion by an intermediate angularly inclined portion, said angularly inclined portion having a bearing engaged by said projecting rounded head of the stud in the end of the ceramic tube and whereby pressure exerted by said ceramic tube is applied to said angularly inclined portion of said projecting arm of said switch spring.

References Cited in the le of this patent UNITED STATES PATENTS 1,651,972 Smallen Dec. 6, 1927 1,678,407 Spencer July 24, 1928 1,780,758 Leupold Nov. 4, 1930 1,914,675 Satchwell .Tune 20, 1933 1,995,385 Foote Mar. 26, 1935 2,185,623 Beam Jan. 2, 1940 2,210,526 Burling Aug. 6, 1940 2,262,667 Dafforn et al Nov. 11, 1941 2,481,265 Van Denberg et al Sept. 6, 1949 2,627,565 Smith Feb. 3, 1953 2,676,224 Stephenson Apr. 20, 1954 2,705,745 Matthysse et al Apr. 5, 1955 2,809,523 Burling et al Oct. 15, 1957 2,817,732 Reingruber Dec. 24, 1957 2,856,489 Bletz Oct. 14, 1958 FOREIGN PATENTS 522,704- Great Britain June 25, 1940 

